Drill pipe vibration control in rotary drilling

ABSTRACT

A method for drilling a well using high-speed rotation of the drill bit and drill pipe wherein catastrophic vibration of the drill pipe during high speed rotation is at least in part prevented by the use of a drilling fluid whose ratio scar width/(plastic viscosity)1/2 is no greater than about 4.

I Unlted States Patent [151 3,635,294 Faulk et al. 45 Ja 18, 1972 [5 1DRILL PIPE VIBRATION CONTROL IN THER BLICATIONS ROTARY DRILLING MudControl And Design by Homer & Kimbrell The I72] Inventors: Joseph H.Fuulk; ,Iurgen J. Hanke, both of Petroleum Engmeer Reference Annual 1949pages 68 Dallas; John H. Strlegler, Richardson, all hmugh 78 f o TexPrimary Examiner-Ernest R. Purser [73] Assignee: Atlantic RichfieldCompany, New York, AltorneyBlucher S.Tharp and Roderick W. MacDonald[22] Filed: Apr. 29, 1970 ABSTRACT [2]] Appl' 33084 A method fordrilling a well using high-speed rotation of the drill bit and drillpipe wherein catastrophic vibration of the [52] U.S.Cl ..l75/65,175/56rill pip during g speed rotation is a! least in p [51] Int.Cl..E21b21/04 prevented by the use of a drilling fluid whose ratio scar 58Field ol'Search ..l75/38, 56, 65-72 wi th/( l viscosity)isnogreaterthanab0ut4- [56] References Cited 7 Claims No Drawings UNITED STATES PATENTS2,717,763 9/1955 Bodine ..175/56X DRILL PIPE VIBRATION CONTROL IN ROTARYDRILLING BACKGROUND OF THE INVENTION Heretofore in rotary drilling awellbore in the earth, the drilling bit and the drill pipe whichsupports the bit in the wellbore are both conventionally rotated duringdrilling at rates of from about 100 to about 250 r.p.m. Such drillingrigs, in the petroleum industry, generally drill boreholes havingdiameters of from about 8% to about 13% inches.

As an exploratory tool, it can be desirable to employ what is known as afslimhole" drilling technique wherein the borehole has a diameter of upto about 6 inches, preferably from about 2 to about 4 inches. With slimhole drilling it is desirable to use higher than conventional rotationrates for the drill bit. For example, rotation rates of at least 400r.p.m. and as high as 1,500 to 3,000 r.p.m. are desirably employed toachieve shorter drilling time.

By drilling small diameter boreholes with high-rotation speed, largernumbers of exploratory wells can be drilled more economically. Inaddition, the rig used is lighter thereby allowing for more economicalmovement of the rig from one drilling location to another.

However, an omnipresent problem with the high-rotation rates of thedrill pipe in the small diameter borehole has been what is termed"catastrophic" vibration of the drill pipe. At rotation rates of greaterthan 400 r.p.m. the drill pipe tends to bounce from one side of theborehole to the other at a faster and faster rate until catastrophicvibration sets in and results in failure of the drill pipe, usually bytwisting off one section of drill pipe from an adjacent section of drillpipe at their coupling joint.

Thus, slim hole drilling using the most economical rotation rate for thedrilling bit and pipe is not feasible from a practical standpoint unlesscatastrophic vibration of the drill pipe during rotation is avoided.

SUMMARY OF THE INVENTION It has now been found that the drilling fluidemployed in the slim hole drilling process can be an aid in preventingcatastrophic vibration of the drill pipe if the drilling fluid has aratio of its scar width to the square root of its plastic viscosity,(plastic viscosity), which is no greater than about 4, preferably equalto or less than 4.

It has been further found that additional aids in preventingcatastrophic vibration of the drill pipe include maintaining the Ph ofthe drilling fluid at a value no greater than about 9 and/or maintainingthe total of undissolved solid material having a specific gravity of nogreater than 3.0, which material is dispersed in the drilling fluid, ata value no greater than about 14 weight per cent based on the totalweight of the drilling fluid.

By following the teachings of this invention, a drilling fluid isobtained which can be an aid in preventing, if not totally preventing,catastrophic vibration of the drill pipe during rotation thereof atspeeds of at least 400 r.p.m., including, but not limited to, speeds upto 3,000 r.p.m.

Accordingly, it is an object of this invention to provide a new andimproved method for drilling a wellbore at high-rotation speeds whileavoiding catastrophic vibration of the drill pipe. It is another, objectto provide a new and improved method for preventing catastrophicvibration of drill pipe when rotated at speeds of at least 400 r.p.m. Itis another object to provide a new and improved method for drilling awellbore utilizing high-speed rotation of the drill pipe and bit and adrilling fluid which aids in preventing catastrophic vibration of therotating drill pipe.

Other aspects, objects, and advantages of this invention will beapparent to those skilled in the art from this disclosure and theappended claims.

DETAILED DESCRIPTION OF THE INVENTION The ratio of scar width/(plasticviscosity)" is determined according to this invention by first obtaininga scar width value for the drilling fluid. This is done using an EP MudTester model 211 which is available commercially from the BaroidDivision of the National Lead Company. This tester is designed tomeasure the lubricating properties of drilling fluids by mounting ahardened steel test cup (Rockwell C scale hardness of 58-62) on arotating shaft and forcing a steel wear block (Rockwell C scale hardnessof 58-62) against the test cup with a predetermined load while the testcup and wear block are immersed in the drilling fluid being tested. Theload is applied with a torque arm that is operatively connected to thewear block, the torque arm containing a torque gauge calibrated in inchpounds. The friction load is read on an ammeter scale indicating theelectrical current consumption of the driving motor. The motor is run at1,400 r.p.m. which amounts to a surface velocity of the test cup of507feet per minute, the test cup diameter being 1.378 inches. Each testcup is used only once and a fresh spot is selected on the wear block foreach run. 1

In the actual test itself, a friction load corresponding to three ampsis applied with the torque arm and the run continued for 20 secondsholding the ammeter reading constant by increasing the load applied tothe torque arm. The width of the scar formed on the wear block by thetest cup is then measured in hundredths of an inch. Each test is carriedout under ambient conditions of temperature and pressure usingsufficient drilling fluid to completely immerse the test cup.

After the scar width is measured, the plastic viscosity of the drillingfluid is obtained in the conventional manner using a l l5-voltmotor-driven viscometer and rotor sleeve and speeds of 300 and 600r.p.m. as fully and completely disclosed in the American Petroleumlnstitutes Standard Procedure for Testing Drilling Fluid Bulletin, APIRP 133, First Edition, Nov., 1962, issued by American PetroleumInstitute Division of Production Dallas, Dallas, Texas, Pages 5 and 6.

The determination of plastic viscosity of drilling fluids in the mannerdescribed above is a conventional procedure well known in the art, andgenerally involves immersing the rotor sleeve of the viscometer in thedrilling fluid up to the line inscribed on the sleeve, rotating thesleeve at 600 r.p.m. and reading the dial when it reaches a steady valuefollowed by shifting the rotating speed from 600 to 300 r.p.m. and againreading the dial when it reaches its steady value. Plastic viscosity incentipoises is the 600 r.p.m. reading minus the 300 r.p.m. reading.

The square root of the plastic viscosity is then taken and divided intothe scar width. If the resulting value is no greater than about 4 thedrilling fluid has adequate capacity for at least aiding in preventingcatastrophic vibration of rapidly rotating drill pipe.

If the drilling fluid does not meet the above ratio requirement, thecomposition of the drilling fluid can be altered to meet thatrequirement. For example, the plastic viscosity can be increased byadding to the drilling fluid varying amounts or combinations ofbentonite, carboxy-methyl-cellulose, attapulgite, and other clays as iswell known in the art. Similarly, the removal of these materials candecrease the plastic viscosity.

The scar width value can be varied by increasing or decreasing thelubricity of the drilling fluid. This can be achieved by adding to orremoving from the drilling fluid one or more materials which have alubricating function. For example, to reduce the scar width,conventional additives known in the art as Extreme Pressure (EP)additives can be employed. Such additives are fully and completelydisclosed in the Society of Petroleum Engineers of AIME Paper No. 1152-6, 1958, entitled Increased Drill Bit Life Through Use of ExtremePressure Lubricant Drilling Fluid, by Rosenberg and Tailleur.

Suitable EP additives include sulfurized diisobutylene, mixtures ofasphalt and bentonite, mixtures of asphalt and sulfurized diisobutylene,mixtures of asphalt and lead sulphite, mixtures of asphalt andsulfurized fatty acids, mixtures of fatty acids, linseed oil, castoroil, sulfurized fatty acids, sulfurized lard oil, sulfurized glyceroltrioleate, alkali metal oleates, oleic acid, sulfurized oleic acid,sulfurized tall oil, and the like.

The drilling fluids employed can be either oil base or water base orcombinations thereof such as water-in-oil or oil-inwater emulsions whichare all known in the art. The scar width and plastic viscosity of thesedrilling fluids, whether they contain oil or water or combinationsthereof, can be varied in order to meet the ratio requirements of thisinvention by using the teachings set forth hereinabove and/or othertechniques known in the art.

Drilling fluid or fluids which meet the ratio requirement of thisinvention can be employed in the drilling process as the sole drillingfluid, substantially the only drilling fluid present, or in any lesseramount in combination with other drilling fluids which do not meet theratio requirement so long as the drilling fluid or fluids which do meetthe ratio requirement are employed in the drilling process in an amountat least sufficient to aid in preventing catastrophic vibration of thedrill pipe. Generally, the drilling fluid or fluids meeting the ratiorequirement of this invention will be employed in a major amountrelative to other drilling fluids used.

It has further been found that in addition to meeting the ratiorequirement of this invention, the ability of a drilling fluid to combatcatastrophic vibration of the drill pipe at rotation rates of greaterthan 400 r.p.m. is enhanced if the drilling fluid has a Ph value of nogreater than 9 and/or the drilling fluid contains undissolvedparticulate solid material (having a specific gravity of less than 3.0)dispersed therein in amounts no greater than about 14 weight per centbased on the total weight of the drilling fluid which meets the ratiorequirement.

EXAMPLE A drilling fluid composed of a major amount of water, anemulsifying amount of soap, a lubricating amount of sulfurized tall oil,and a minor amount of diesel oil had a scar width of 7.5 hundredths ofan inch and a plastic viscosity of 2.5 centipoises so that its ratioscar width/(plastic viscosity)" equaled 4.74. The scar width and plasticviscosity were determined as set forth hereinabove.

The drilling fluid was employed in drilling a wellbore 3 /4 inches indiameter using a drill pipe having l.9 inches outside diameter and adiamond bit. The drill pipe and bit were rotated at 400 r.p.m.

Eleven hundred feet of wellbore was drilled using the above conditionsand drilling fluid. Catastrophic vibration caused five drill collarseparations and failures.

By adding 3 weight percent bentonite to the above drilling fluid, theratio scar width/( plastic viscosity)" was decreased to 1.5 (scar width6 and plastic viscosity 16). With this drilling fluid, drilling wascontinued under the same Conditions as set forth above in this exampleexcept that the pipe and bit were rotated at 1,100 r.p.m. and nocatastrophic vibration was encountered.

Reasonable variations and modifications are possible within the scope ofthis disclosure without departing from the spirit and scope of thisinvention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a method for drilling a wellbore in the earth wherein the drillingbit and at least part of the drill pipe is rotated during drilling atspeeds of at least about 400 r.p.m., the improvement comprisingemploying at least during drilling a drilling fluid whose ratio scarwidth/(plastic viscosity)" is no greater than about 4, said drillingfluid being employed in an amount at least sufficient to aid inpreventing catastrophic vibration of the drill pipe.

2. A method according to claim 1 wherein said drilling fluid is an oilbase drilling fluid.

3. A method according to claim 1 wherein said drilling fluid is a waterbase drillin fluid. I

4. A method accor ing to claim 1 wherein said ratio lS equal to or lessthan 4.

5. A method according to claim 1 wherein said drilling fluid issubstantially the only drilling fluid employed.

6. A method according to claim 1 wherein said drilling fluid has a pH nogreater than about 9.

7. A method according to claim 1 wherein said drilling fluid hasdispersed therein no greater than about 14 weight percent based on thetotal weight of said drilling fluid of solid material having a specificgravity of no greater than 3.0.

* i k l

2. A method according to claim 1 wherein said drilling fluid is an oilbase drilling fluid.
 3. A method according to claim 1 wherein saiddrilling fluid is a water base drilling fluid.
 4. A method according toclaim 1 wherein said ratio is equal to or less than
 4. 5. A methodaccording to claim 1 wherein said drilling fluid is substantially theonly drilling fluid employed.
 6. A method according to claim 1 whereinsaid drilling fluid has a pH no greater than about
 9. 7. A methodaccording to claim 1 wherein said drilling fluid has dispersed thereinno greater than about 14 weight percent based on the total weight ofsaid drilling fluid of solid material having a specific gravity of nogreater than 3.0.